Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.80   7.538%   $224.5393   $224.54   $224.55   $224.50  
  Purchase #2 $243.28   5.464%   $256.5728   $256.57   $256.55   $256.60  
  Purchase #3 $51.91   9.398%   $56.7885   $56.79   $56.80   $56.80  
  Purchase #4 $126.34   9.683%   $138.5735   $138.57   $138.55   $138.60  
  Purchase #5 $109.39   9.425%   $119.7   $119.70   $119.70   $119.70  
  Purchase #6 $101.97   4.201%   $106.2538   $106.25   $106.25   $106.30  
  Purchase #7 $191.84   10.748%   $212.459   $212.46   $212.45   $212.50  
  7 purchase totals = $1,033.53       $1,114.8869   $1,114.88   $1,114.85   $1,115.00